1. Field of the Invention
The inventive concept relates to optical devices and methods, and, more specifically, to optical waveguides and couplers used to implement optical communications, and methods of manufacturing the optical waveguides and couplers.
2. Description of the Related Art
Optical devices such as optical fibers, optical waveguides and optical couplers are used for high-speed, low-power communication in various devices and systems. Optical interconnections have been used to achieve large-capacity, high-speed and low-power communication in semiconductor memory devices, modules and systems. In such systems, optical fibers can be used to communicate between modules. The optical fibers can be coupled to the memory modules and devices by optical couplers, and the optical signals can be transmitted within modules and memory devices by optical waveguides.
Due to small size requirements, optical interconnections in memory modules, devices and systems typically require that optical waveguides and couplers be integrated into a semiconductor wafer. Conventionally, integrated optical waveguides and couplers are formed on silicon-on-insulator (SOI) substrates, which include a layer of insulating material, such as silicon oxide (SiO2), formed over a single-crystal silicon substrate or wafer. The insulating material layer serves as a bottom cladding layer for the waveguide. A waveguide core material, such as amorphous silicon, having a higher index of refraction than that of the lower cladding layer, is formed on the lower cladding layer. An upper cladding layer, such as a layer of material having a lower index of refraction than that of the core layer, may be formed over and/or around the core layer to complete the waveguide cladding. The upper cladding layer may be another layer of silicon oxide, a layer of polysilicon, or another material having a lower refractive index than the core. For example, in some cases, air may serve as the upper cladding layer.
The SOI wafers in which conventional devices are formed are considerably more expensive than conventional semiconductor wafers. Also, because conventional integrated optical devices are formed in SOI substrates, full integration of the optical devices with other circuitry, such as memory device circuitry, cannot be realized, since such devices are not typically formed on SOI substrates. As a result, the optical devices are typically formed as separate devices on separate chips and/or in separate packages. This results in devices, modules and systems of larger size and complexity, and also of higher relative cost.
As the need for small-size, high-speed, low-power and cost-efficient memory devices, modules and systems continues to increase, there is an increasing need for optical interconnection devices and systems which can be manufactured less expensively, are smaller in size, can operate at high speed and with low power consumption and can be efficiently integrated with the other circuitry on a single chip or wafer.